1. Field of the Invention
The present invention relates to the field of internal combustion engines such as diesel engines, gasoline engines and engines designed to operate on alternate fuels.
2. Prior Art
The present invention is applicable to various types of engines, including diesel engines, gasoline engines and engines intended to operate on alternate fuels. However for purposes of specificity in the disclosure herein, preferred embodiments will first be described with respect to diesel engines, after which the applicability to other types of engines will be described. Accordingly, the prior art with respect to diesel engines will be described herein, it being understood that generally speaking, many of the characteristics of diesel engines described herein translate in various ways to other types of engines.
It is well known that the pollutants produced by diesel engines consist primarily of nitrous oxides (NOx) and unburned hydrocarbons. It is also well known that nitrous oxides form above a particular temperature, or more importantly for the present invention, do not form below the nitrous oxide formation temperature limit. This temperature limit is significantly above the ignition temperature for a diesel fuel-air mixture, though in conventional diesel engines, local temperatures within the combustion chamber frequently exceed the nitrous oxide formation temperature limit for various reasons. The unburned hydrocarbons in a diesel engine exhaust, on the other hand, generally have two primary causes, namely first, the impingement of part of the spray of injected fuel on a relatively cool surface before the fuel has an opportunity to burn, or at least entirely burn, and second, the local injection of fuel into regions of the combustion chamber having inadequate oxygen to locally allow all of the injected fuel to burn. This second cause, of course, helps facilitate the former cause, as the fuel can't burn without adequate oxygen.
Preferably in a diesel engine, a small pre-injection of fuel is used to initiate combustion, with a main injection of fuel occurring shortly thereafter, starting at or near top dead center of the piston in the cylinder. When the piston is in its uppermost position, or near its uppermost position, the injection spray should not be downward onto the top of the piston, as that causes a high content of hydrocarbons in the diesel exhaust, as previously described, as well as possibly damaging the engine. However as the piston moves away from top dead center, the contents in the combustion chamber expand, with the center of those contents generally moving downward at half the rate of the piston. Accordingly, the continued fuel injection in a direction suitable for the top dead center position of the piston is injecting fuel only into the top layer, so to speak, of air in the combustion chamber. This has multiple adverse effects. The concentration of fuel in this limited volume can easily result in local temperatures exceeding the nitrous oxide formation temperature limit. Further, the oxygen in this limited region of the combustion chamber may be consumed, even though adequate oxygen is available therebelow, resulting in incomplete combustion of the fuel and substantial hydrocarbons in the exhaust. The only available control for these effects in prior art engines and operating methods is to try to limit the total injection in relation to the volume and oxygen content of that portion of the combustion chamber volume into which the fuel is injected, thereby providing a limit on the mechanical energy developed during that combustion cycle.
In one prior art injector, spray nozzles in multiple directions are used, with initial injection having a more radial component to better facilitate the proper injection when the piston is at or near top dead center, with a mechanical valve switching the injection flow to injection orifices projecting more toward the piston so that the injection of the fuel can better follow the majority of the remaining oxygen available for combustion. Such an injector could have meaningful advantages, such as in stationary engines operating under a constant load. However the fact that the control is mechanical and has preset limits, restricts its flexibility in engines such as truck engines and the like, which operate throughout a relatively wide range of engine speed and a very wide range of power output.